Flexible CNC belt grinding machine

ABSTRACT

A belt grinding machine is disclosed that includes an automatic pressure and position control systems for robotic grinding and polishing applications. The machine will be combined with off-line programming package, capable of carrying out complicated operations that cannot be performed on traditional types of machines. The multiple contact wheels of the machine give the flexibility to accommodate complicated geometry of workpieces with a large material removal rate (MRR) and great surface finishes. The basic components of this belt grinding machine consists of the followings: a power source, a drive wheel or active wheel driven by a motor, multiple contact wheels; an idler for tensioning and tracking the belt, an active force control device to keep the constant pressure on the workpiece, a proper coated abrasive belt, and a dust collection system.

BACKGROUND OF THE INVENTION

The invention relates to a belt grinding machine with a compliant framewhich has a plurality of contact wheels arranged around a common axis ofrotation. The compliance can be set or controlled according to the needfrom the robotic grinding process. The compliance is provided an activepneumatic device and con also be provided by other actuators and sensorcombinations. Existing designs of compliant belt grinders uses a linearguide way to guide the contact wheel frame.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a belt grindingmachine of a kind in which the compliant system of the grinder ispossible with a simple device that allows the motion of the frame whichsupports multiple contact wheels.

According to the invention, this object is achieved with a rectangular,parallel four-bar linkage connected to an actuator or a passive springfor delivering compliant motion that allows the contact wheels with abelt to yield or compensate automatically based on the change ofgrinding force between the workpiece and the belt.

The belt grinding machine according to the invention makes is possiblenot only to deflect in a simple way, but also to deflect without havingany mechanical interference between the belt grinding machine frame andthe robot with even a large workpiece. By means of the parallelcompliant frame of the four-bar linkage, the grinding force applied to aworkpiece can be well controlled, and wheels of various diameters can becontrolled and used in an optimized way.

The grinder in this invention is designed for any part in roboticgrinding and polishing applications. The travel compliance and excellentmedia access allows a robot to easily manipulate workpiece of any shapeover the abrasive belts. As shown in FIG. 1, the following features makethe grinder in this invention unique:

-   -   Active and continues force control (passive option available);    -   Direct contact wheel and grinding head displacement measurement        using LVDT or laser    -   Laser detect belt centering and auto-adjustment    -   Changeable multi-geometry contact wheel in grinding process    -   Active pneumatic contact wheel with adjustable contact stiffness    -   Shaped pneumatic contact wheels    -   Modular design make the different combination easy for different        geometry workpieces    -   Accurate and continuous belt speed control (0 to 8000 SFPM)    -   Direct gear drive    -   Different belt width in one machine;    -   Active adjustable pneumatic belt tensioning    -   Both linear and rotational travel floating belt heads    -   Stationary belt guards

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a belt grinder is shown. The abrasive belt (notshown in the drawing) runs around driven wheel 1 which also serve astracking wheel, tension wheel 3 and contact wheels 4. The abrasive beltis guided round at least three contact wheels 4. The contact wheels canbe changed during grinding by contact wheel turntable 5 to adapt theshape of workpiece. Driven wheel 1 is actuated by motor 2. To carry outthe desired surface grinding, the workpiece (not shown in the drawing)runs on the abrasive belt on different size and shape contact wheels.The abrasive belt is designed as an endless belt. The driven wheel,tension wheel and contact wheel are aligned parallel to each other, sothat the abrasive belt extends parallel to the contact wheels (grindingzone). The abrasive belt is pressed against the workpiece by means of apressure formed from pneumatic cylinder 6 through parallel bar mechanism7. The pressing force is adjusted by means of a pressure valve toaccomplish different grinding task. The parallel mechanism and cylinderstand 8 are mounted on base 9. The length of slide 10 in the bar ofparallel mechanism is adjustable to adapt the different length ofabrasive belt.

1. A belt grinding machine comprising a compliant frame of a parallelfour-bar linkage which carries multiple contact wheels of variousdiameter and width, and hardness. Active force sensing, compliancecontrol and automatic wheel size control allows belt grinding to beperformed on various workpieces with an enhanced productivity.
 2. A beltgrinding machine as claimed in claim 1, wherein the compliance of thefour-bar linkage is provided by a pneumatic actuator or a device.
 3. Abelt grinding machine as claimed in claim 1, wherein the compliantlinkage oscillates according to the change of grinding process force. 4.A belt grinding machine as claimed in claim 1, wherein the frame carriesa group of contact wheels of various properties with the grinding beltwrapping around the wheel system.
 5. A belt grinding machine as claimedin claim 4, wherein the wheels are arranged around a common axis ofrotation with an active motor to position the wheels so that the rightcontact wheel that fits the shape and size of the workpiece to bemachined will be aligned automatically in a position that grinding canbe performed efficiently with the compliance system working properly. 6.A belt grinding machine as claimed in claim 5, wherein the rotation ofthe contact wheel group is CNC-based.
 7. A belt grinding machine asclaimed in claim 4, wherein the frame carries a tensioning wheel.
 8. Abelt grinding machine as claimed in claim 4, wherein the frame carries atracking wheel.
 9. A belt grinding machine as claimed in claim 1,wherein the grinding force sensing means includes a detection means fordetecting grinding force variations in the signal output from the forcesensor to the signal-processing unit means and determines the deflectionof the contact wheel based on the process requirements.